This research explores the origins of the link between gesture and speech by focusing on the dynamic properties of the development of infant vocal and motor systems. The study addresses specific hypotheses derived from a model of infant vocal and motor system as coupled oscillators that can mutually entrain one another. To examine the ways in which the relative strength and stability of behaviors in the component systems influence entrainment and lead to developmental changes in the strength and specificity of vocal-motor coordination, vocalizations, rhythmic limb movements, speech, gestures, and vocal- motor and speech-gesture coordinations will be observed in infants biweekly between the ages of 2 and 19 months. Thirty full-term, normally-developing infants will be videotaped at home for 45 minutes in naturalistic and semistructured play contexts. All infant vocalizations, rhythmic limb movements, words, and gestures will be coded. Data analyses will focus on normative and milestone-related developmental change in these phenomena, patterns of co-occurrence between vocal and motor behaviors as a function of age, and the relationship between early communicative milestone achievement and the nature and temporal organization of vocal-motor coordination. This research will also assess individual differences among infants in vocal- manual coordination patterns and their potential relationship to later communication. The fact that variation in gesture use has been shown to relate to communicative delay suggests the possibility that individual variability in early vocal-manual coordination may have diagnostic significance for later communication disorders. Identification of the typical pattern and normal range of variation in early vocal-manual coordination will provide normative information required for future diagnostic research.